H.G. Parkinson

Doctor of Philosophy, Oxford University, Trinity 1987

Measurements of Wind Flow Over Models of a Hill

Summary

This thesis describes an investigation into wind flow over hills, and its relevance to wind turbine siting. It forms part of an international collaborative project known as the Askervein experiment, carried out under the auspices of the International Energy Agency which includes full scale measurements over Askervein hill, experiments in wind tunnels, and also numerical flow modelling. The present research forms part of the wind tunnel work, in which experimental techniques are examined, and detailed measurements of the flow structure over a hill are obtained. Models at three scales have been tested in the 4m x 2m industrial aerodynamics wind tunnel at Oxford.

The experiments show that for the range of scales tested, the model flow can be made to reproduce the full scale behaviour. The surface texture of the model is critical if the full scale flow behaviour is a roughness Reynolds number based on the aerodynamic characteristics of the surface texture. For values of roughness Reynolds number greater than about 2.5 the flow is Reynolds number independent and similarity with the atmospheric boundary layer is maintained. The flow simulation created by this method often requires the matching of the geometric similarity of the surface texture to be relaxed.

Results from experiments on the models obtained by the other project participants were compared with the author's results to assess the effect of wind tunnel techniques. The independent results show good agreement, vindicating the test methods. Good agreement between the wind tunnel results and the full scale data was found, showing that a wind tunnel can be used as an accurate method to predict changes in both mean and turbulent properties as the flow passes over the hill.

Comparison of the present results with the numerical model of Zeman & Jensen show generally good agreement, increasing the confidence in the theoretical interpretation of the model. The results show the importance of an accurate description of the wind at a prospective wind turbine site, both in terms of maximising energy capture, and in terms of designing for a reasonable fatigue life in a turbulent environment.

(no thesis available)